It isn't just the dearth of volume and volatility that is weighing on Wall Street bond-trading desks. Declining velocity is, too.

Bond velocity is similar to the velocity of money. But instead of measuring the rate at which money is exchanged for goods and services, it measures the rate at which bonds are traded. Simply put, it is the ratio of trading to outstanding bonds.

And just as the velocity of money has been in decline, bond velocity has been falling. From 2002 through 2008, the average daily volume of bond trading was more than 3% of the total outstanding stock of bonds, based on data from the Securities Industry and Financial Markets Association. Following the financial crisis, however, bond velocity dropped off sharply.

Last year, it was just 2.03%. This year it has fallen to 1.79%. That compounds the negative impact of low issuance, so that traders are buying and selling a smaller share of a bond market whose growth has slowed.

Structural changes at banks are undoubtedly weighing on velocity. Banks have moved billions of dollars of bonds into held-to-maturity portfolios, meaning they are unlikely to be traded. Also, the "Volcker rule" bans short-term proprietary trading, which makes bonds less likely to change hands. And treasuries banks hold to meet minimum liquidity requirements are also unlikely to move.

The Federal Reserve is playing a role, as well. Thanks to quantitative easing, it now owns a sizable portion of the bond market. And since the Fed doesn't plan to sell its QE portfolio, bonds sold to the Fed effectively lie dormant.

The silver lining is that the end of quantitative easing might allow velocity to rise somewhat. That would be good news for bond traders—and the banks that employ them.